Catalytic processes and systems for base oil production using zeolite ssz-32x

ABSTRACT

Processes and catalyst systems are provided for dewaxing a hydrocarbon feedstock to form a lubricant base oil. A layered catalyst system of the present invention may comprise a first hydroisomerization dewaxing catalyst disposed upstream from a second hydroisomerization dewaxing catalyst. Each of the first and second hydroisomerization dewaxing catalysts may be selective for the isomerization of n-paraffins. The first hydroisomerization catalyst may have a higher level of selectivity for the isomerization of n-paraffins than the second hydroisomerization dewaxing catalyst. At least one of the first and second hydroisomerization dewaxing catalysts comprises small crystallite zeolite SSZ-32x.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/299,463, now U.S. Pat. No. 9,677,016, which is a continuation of U.S.patent application Ser. No. 13/159,695, now U.S. Pat. No. 8,790,507,which claims priority from U.S. Provisional Appl. No. 61/359,720, theentire disclosures of which are herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to processes and systems for dewaxing hydrocarbonfeedstocks.

BACKGROUND OF THE INVENTION

High quality lubricating oils are critical for the operation of modernmachinery and motor vehicles. However, current crude oil supplies areinadequate to meet present demands for such lubricants. Therefore, it isnecessary to upgrade crude oil fractions otherwise unsuitable forlubricant manufacture. As an example, high-quality lubricating oils mustoften be produced from waxy feeds. Numerous processes have been proposedfor producing lubricating base oils by upgrading ordinary and lowquality feedstocks.

Hydrocarbon feedstocks may be catalytically dewaxed by hydrocracking orhydroisomerization. Hydrocracking generally leads to a loss in yield dueto the production of lower molecular weight hydrocarbons, such as middledistillates and even lighter C⁴⁻ products, whereas hydroisomerizationgenerally provides higher yields by minimizing cracking.

U.S. Pat. No. 7,384,538 to Miller discloses hydroisomerization of waxyfeed for base oil production in an isomerization zone comprising acatalyst bed having at least two isomerization catalysts, wherein afirst catalyst has a channel diameter of at least 6.2 A, and a secondcatalyst has a channel diameter not more than 5.8 A. U.S. PublicationNo. 20080083657 (Zones et al.) discloses dewaxing a hydrocarbon feedwith a metal-modified small crystallite MTT framework molecular sieve.U.S. Publication No. 20090166252 (Daage et al.) discloses lube basestockproduction using two isomerization catalysts, wherein a first catalysthas a Constraint Index (CI) of not more than 2, and a second catalysthas a CI greater than 2.

Apart from product yield, another important factor in the catalyticproduction of base oil is the minimization of catalyst aging. In thisregard, U.S. Pat. No. 5,951,848 discloses the use of a two catalystsystem comprising a hydrotreating catalyst and a dewaxing catalyst. Theaging of the dewaxing catalyst may be slowed by the presence of thehydrotreating catalyst layer.

U.S. Pat. Nos. 6,468,417 and 6,468,418, both to Biscardi et al.,disclose the production of lube oil having a reduced tendency to form ahaze by a process including contacting a dewaxed lube stock or base oilfeed with a solid sorbent to produce a dehazed base oil having a reducedcloud point relative to that of the dewaxed lube stock or base oil feed.

There is a continuing need for improved dewaxing processes and catalystsystems showing increased isomerization selectivity and conversion ofwaxy hydrocarbon feedstocks for the production of valuable Group II andGroup III base oils.

SUMMARY OF THE INVENTION

This invention relates to processes for efficiently convertingwax-containing hydrocarbon feedstocks into high-grade products,including lubricant base oils having a low pour point, a low cloudpoint, a low pour-cloud spread, and a high viscosity index (VI). Suchprocesses employ a layered catalyst system comprising a plurality ofhydroisomerization dewaxing catalysts. Hydroisomerization convertsaliphatic, unbranched paraffinic hydrocarbons (n-paraffins) toisoparaffins and cyclic species, thereby decreasing the pour point andcloud point of the base oil product as compared with the feedstock. Inan embodiment, a layered catalyst system of the present invention mayfurther comprise a hydrotreating catalyst as a guard layer, whereby“aging” of the hydroisomerization catalysts is decelerated, and base oilproduct yield can be maintained for longer periods of time, as comparedwith conventional processes, at a temperature in the range from about450° F. to about 725° F.

According to one aspect of the present invention there is provided aprocess for catalytically dewaxing a waxy hydrocarbon feedstockcomprising contacting the hydrocarbon feedstock in a firsthydroisomerization zone under first hydroisomerization dewaxingconditions with a first hydroisomerization catalyst to provide a firstisomerization stream, and contacting at least a portion of the firstisomerization stream in a second hydroisomerization zone under secondhydroisomerization dewaxing conditions with a second hydroisomerizationcatalyst to provide a second isomerization stream. Each of the first andsecond hydroisomerization catalysts may comprise a molecular sieve and aGroup VIII metal. The molecular sieve of at least one of the firsthydroisomerization catalyst and the second hydroisomerization catalystmay comprise zeolite SSZ-32x having, after calcination, an X-raydiffraction pattern substantially as in Table 4, infra.

In an embodiment, the present invention provides a process forcatalytically dewaxing a waxy hydrocarbon feedstock comprisingcontacting the hydrocarbon feedstock in a first hydroisomerization zoneunder first hydroisomerization dewaxing conditions with a firsthydroisomerization catalyst to provide a first isomerization stream, andcontacting at least a portion of the first isomerization stream in asecond hydroisomerization zone under second hydroisomerization dewaxingconditions with a second hydroisomerization catalyst to provide a secondisomerization stream. Each of the first hydroisomerization catalyst andthe second hydroisomerization catalyst may comprise a 1-D, 10-ringzeolite and a Group VIII metal. At least one of the firsthydroisomerization catalyst and the second hydroisomerization catalystmay be doped with a metal modifier selected from the group consisting ofMg, Ca, Sr, Ba, K, La, Pr, Nd, Cr, and combinations thereof. The firstand second hydroisomerization catalysts may be disposed in the samereactor. The zeolite of the first hydroisomerization catalyst maycomprise SSZ-32x having, after calcination, an X-ray diffraction patternsubstantially as in table 4, infra.

In another embodiment, the present invention provides a layered catalystsystem comprising a first hydroisomerization zone comprising a firsthydroisomerization catalyst, and a second hydroisomerization zonecomprising a second hydroisomerization catalyst. Each of the first andsecond hydroisomerization catalysts may comprise a molecular sieve and aGroup VIII metal. The molecular sieve of at least one of the firsthydroisomerization catalyst and the second hydroisomerization catalystmay be doped with a metal modifier selected from the group consisting ofMg, Ca, Sr, Ba, K, La, Pr, Nd, Cr, and combinations thereof. Themolecular sieve of at least one of the first hydroisomerization catalystand the second hydroisomerization catalyst may comprises zeolite SSZ-32xhaving, after calcination, an X-ray diffraction pattern substantially asin Table 4, infra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically represents a system for hydrocarbon dewaxingprocesses, according to an embodiment of the present invention;

FIG. 2A schematically represents a layered dewaxing catalyst system,according to an embodiment of the present invention;

FIG. 2B schematically represents a layered dewaxing catalyst systemhaving the inverse configuration of the system of FIG. 2A;

FIGS. 3A-B each schematically represents a catalytic dewaxing systemhaving a single dewaxing catalyst; and

FIG. 3C schematically represents a layered catalytic dewaxing system,according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a hydrocarbon dewaxing process whichinvolves contacting a hydrocarbon feedstock with a layered catalystsystem comprising a first hydroisomerization catalyst and a secondhydroisomerization catalyst. In an embodiment, the present inventionalso provides a catalyst system for dewaxing a hydrocarbon feedstock,wherein the first hydroisomerization catalyst may be upstream from thesecond hydroisomerization catalyst.

In an embodiment, the first hydroisomerization catalyst may be in afirst hydroisomerization layer or zone of the catalyst system, and thesecond hydroisomerization catalyst may be in a second hydroisomerizationlayer or zone of the catalyst system. The first hydroisomerizationcatalyst and the second hydroisomerization catalyst may be in the samereactor. The first hydroisomerization catalyst and the secondhydroisomerization catalyst may be disposed in separate beds in the samereactor. Alternatively, at least a portion of the firsthydroisomerization catalyst may be in the same bed as at least a portionof the second hydroisomerization catalyst, and/or at least a portion ofthe second hydroisomerization catalyst may be in the same bed as atleast a portion of the first hydroisomerization catalyst.

Applicants have now demonstrated that layered catalyst systems of thepresent invention comprising first and second hydroisomerizationcatalysts with a combined volume, V, can provide superior results, e.g.,overall greater isomerization selectivity as determined by increasedyield and/or higher viscosity index (VI) of the base oil product, ascompared with the same volume (V) of either the first hydroisomerizationcatalyst alone or the second hydroisomerization catalyst alone.

In an embodiment, catalyst systems of the present invention may furthercomprise a hydrotreating catalyst. The hydrotreating catalyst maycomprise, and may function as, a guard layer or guard bed. Thehydrotreating catalyst of the guard layer may be disposed upstream fromthe first hydroisomerization catalyst. The hydrotreating catalyst of theguard layer may serve to protect the first and second hydroisomerizationcatalysts from contaminants in the feedstock that could deactivate thehydroisomerization catalysts. Thus, the presence of the guard layer cansubstantially increase the longevity of the first and secondhydroisomerization catalysts. In an embodiment, the guard layer may bedisposed in the same reactor as the first and second hydroisomerizationcatalysts. Accordingly, processes of the present invention may bepracticed in a single reactor.

In an embodiment, the reaction conditions for processes of the presentinvention may be determined, inter alia, by the temperature required forthe first and second hydroisomerization catalysts to achieve a targetpour point of a desired base oil product of the invention. Typically,the hydroisomerization catalysts may have an operating temperature inthe range from about 390° F. to about 800° F., and usually from about550° F. to about 750° F. In practice, the process temperature may dependon various other process parameters, such as the feed composition, thefeed rate, the operating pressure, the formulation of the catalystsystem, and the “age” of the hydroisomerization catalysts.

Definitions

The following terms used herein have the meanings as definedhereinbelow, unless otherwise indicated.

The term “hydrotreating” refers to processes or steps performed in thepresence of hydrogen for the hydrodesulphurization,hydrodenitrogenation, hydrodemetallation, and/or hydrodearomatization ofcomponents (e.g., impurities) of a hydrocarbon feedstock, and/or for thehydrogenation of unsaturated compounds in the feedstock. Depending onthe type of hydrotreating and the reaction conditions, products ofhydrotreating processes may have improved viscosities, viscosityindices, saturates content, low temperature properties, volatilities anddepolarization, for example.

The terms “guard layer” and “guard bed” may be used herein synonymouslyand interchangeably to refer to a hydrotreating catalyst orhydrotreating catalyst layer. The guard layer may be a component of acatalyst system for hydrocarbon dewaxing, and may be disposed upstreamfrom at least one hydroisomerization catalyst.

As used herein the term “molecular sieve” refers to a crystallinematerial containing pores, cavities, or interstitial spaces of a uniformsize in which molecules small enough to pass through the pores,cavities, or interstitial spaces are adsorbed while larger molecules arenot. Examples of molecular sieves include zeolites and non-zeolitemolecular sieves such as zeolite analogs including, but not limited to,SAPOs (silicoaluminophosphates), MeAPOs (metalloaluminophosphates),AlPO₄, and ELAPOs (nonmetal substituted aluminophosphate families).

As used herein, the term “pour point” refers to the temperature at whichan oil will begin to flow under controlled conditions. The pour pointmay be determined by, for example, ASTM D5950-96.

“Target pour point” means the desired or required pour point of alubricant base oil product. The target pour point is generally less thanabout −10° C., and typically in the range from about −10° C. to −50° C.

As used herein, “cloud point” refers to the temperature at which a lubeoil sample begins to develop a haze as the oil is cooled under specifiedconditions. The cloud point of a lube base oil is complementary to itspour point. Cloud point may be determined by, for example, ASTMD5773-95.

The “pour point/cloud point spread,” or “pour-cloud spread” of a baseoil, refers to the spread or difference between the cloud point and thepour point, and is defined as the cloud point minus the pour point, asmeasured in ° C. Generally, it is desirable to minimize the spreadbetween the pour and cloud points.

Unless otherwise specified, the Periodic Table of the Elements referredto in this disclosure is the CAS version published by the ChemicalAbstract Service in the Handbook of Chemistry and Physics, 72^(nd)edition (1991-1992).

“Group VIII metal” refers to elemental metal(s) selected from Group VIIIof the Periodic Table of the Elements and/or to metal compoundscomprising such metal(s).

Unless otherwise specified, the “feed rate” of a hydrocarbon feedstockbeing fed to a catalytic reaction zone is expressed herein as the volumeof feed per volume of catalyst per hour, which may be referred to asliquid hourly space velocity (LHSV) with units of reciprocal hours(hr⁻¹).

The term “hydroisomerization” refers to a process in which n-paraffins(n-alkanes) are isomerized to their more branched counterparts in thepresence of hydrogen over a hydroisomerization (dewaxing) catalyst.

Unless otherwise specified, the recitation of a genus of elements,materials, or other components from which an individual component ormixture of components can be selected is intended to include allpossible sub-generic combinations of the listed components and mixturesthereof. Also, “include” and its variants are intended to benon-limiting, such that recitation of items in a list is not to theexclusion of other like items that may also be useful in the materials,compositions, and methods of this invention.

Properties for the materials described herein may be determined asfollows:

-   -   (a) SiO₂/Al₂O₃ Ratio (SAR): determined by ICP elemental        analysis. A SAR of infinity (Go) represents the case where there        is no aluminum in the zeolite, i.e., the mole ratio of silica to        alumina is infinity. In that case the molecular sieve is        comprised essentially of all silica.    -   (b) Surface area: determined by N₂ adsorption at its boiling        temperature. BET surface area is calculated by the 5-point        method at P/P₀=0.050, 0.088, 0.125, 0.163, and 0.200. Samples        are first pre-treated at 400° C. for 6 hours in the presence of        flowing, dry N₂ so as to eliminate any adsorbed volatiles like        water or organics.    -   (c) Micropore volume: determined by N₂ adsorption at its boiling        temperature. Micropore volume is calculated by the t-plot method        at P/P₀=0.050, 0.088, 0.125, 0.163, and 0.200. Samples are first        pre-treated at 400° C. for 6 hours in the presence of flowing,        dry N₂ so as to eliminate any adsorbed volatiles like water or        organics.    -   (d) Mesopore pore diameter: determined by N₂ adsorption at its        boiling temperature. Mesopore pore diameter is calculated from        N₂ isotherms by the BJH method described in E. P. Barrett, L. G.        Joyner and P. P. Halenda, “The determination of pore volume and        area distributions in porous substances. I. Computations from        nitrogen isotherms.” J. Am. Chem. Soc. 73, 373-380, 1951.        Samples are first pre-treated at 400° C. for 6 hours in the        presence of flowing, dry N₂ so as to eliminate any adsorbed        volatiles like water or organics.    -   (e) Total pore volume: determined by N₂ adsorption at its        boiling temperature at P/P₀=0.990. Samples are first pre-treated        at 400° C. for 6 hours in the presence of flowing, dry N₂ so as        to eliminate any adsorbed volatiles like water or organics.

Where permitted, all publications, patents and patent applications citedin this application are incorporated by reference herein in theirentirety, to the extent such disclosure is not inconsistent with thepresent invention.

Hydrotreating Catalysts

In an embodiment, catalyst systems of the present invention may includea hydrotreating catalyst, e.g., in the form of a guard layer.Hydrotreating catalysts of the present invention may comprise arefractory inorganic oxide support and a Group VIII metal. The oxidesupport may also be referred to herein as a binder. The support of thehydrotreating catalyst may be prepared from or comprise alumina, silica,silica/alumina, titanic, magnesia, zirconia, and the like, orcombinations thereof. The catalyst support may comprise amorphousmaterials, crystalline materials, or combinations thereof. Examples ofamorphous materials include, but are not limited to, amorphous alumina,amorphous silica, amorphous silica-alumina, and the like.

In an embodiment, the support may comprise amorphous alumina. When usinga combination of silica and alumina, the distribution of silica andalumina in the support may be either homogeneous or heterogeneous. Insome embodiments, the support may consist of an alumina gel in which isdispersed the silica, silica/alumina, or alumina base material. Thesupport may also contain refractory materials other than alumina orsilica, such as for example other inorganic oxides or clay particles,provided that such materials do not adversely affect the hydrogenationactivity of the final catalyst or lead to deleterious cracking of thefeedstock.

In a subembodiment, silica and/or alumina will generally comprise atleast about 90 wt % of the support of the hydrotreating catalyst, and insome embodiments the support may be at least substantially all silica orall alumina. Regardless of the type of support material in thehydrotreating catalyst, the hydrotreating catalyst used in processes andcatalyst systems of the present invention will typically have lowacidity. Where appropriate, the acidity of the support can be decreasedby treatment with alkali and/or alkaline earth metal cations.

Various crystalline and non-crystalline catalyst support materials thatmay be used in practicing the present invention, as well as thequantification of their acidity levels and methods for neutralizing acidsites in the catalyst support are described in co-pending, commonlyassigned U.S. patent application Ser. No. 12/574,500 filed Oct. 9, 2009entitled Novel process and catalyst system for improving dewaxingcatalyst stability and lubricant oil yield, the disclosure of which isincorporated by reference herein in its entirety.

The Group VIII metal component(s) of the hydrotreating catalyst maycomprise platinum, palladium, or combinations thereof. In an embodiment,the hydrotreating catalyst comprises platinum and palladium with a Pt:Pdratio in the range from about 5:1 to about 1:5, typically from about 3:1to about 1:3, and often from about 1:1 to about 1:2. The Group VIIImetal content of the hydrotreating catalyst may generally be in therange from about 0.01 wt % to about 5 wt %, typically from about 0.2 wt% to about 2 wt %. In an embodiment, the hydrotreating catalyst maycomprise platinum at a concentration in the range from about 0.1 toabout 1.0 wt %, and palladium at a concentration in the range from about0.2 to about 1.5 wt %. In a subembodiment, the hydrotreating catalystmay comprise about 0.3 wt % platinum and about 0.6 wt % palladium.Hydrotreating catalysts of the present invention generally exhibitsulfur tolerance as well as high catalytic activity.

In an embodiment, the Group VIII metal of the hydrotreating catalyst maybe dispersed on the inorganic oxide support. A number of methods areknown in the art to deposit platinum and/or palladium metal, orcompounds comprising platinum and/or palladium, onto the support; suchmethods include ion exchange, impregnation, and co-precipitation. In anembodiment, the impregnation of the support with platinum and/orpalladium metal may be performed at a controlled pH value. The platinumand/or palladium is typically added to the impregnating solution as ametal salt, such as a halide salt, and/or an amine complex, and/or asalt of a mineral acid. Ammonium salts have been found to beparticularly useful in preparing solutions for Group VIII metalimpregnation. Other examples of metal salts that may be used includenitrates, carbonates, and bicarbonates, as well as carboxylic acid saltssuch as acetates, citrates, and formates.

Optionally, the impregnated support may be allowed to stand with theimpregnating solution, e.g., for a period in the range from about 2 toabout 24 hours. Following impregnation of the oxide support with theGroup VIII metal, the impregnated support can be dried and/or calcined.After the hydrotreating catalyst has been dried and calcined, theprepared catalyst may be reduced with hydrogen, as is conventional inthe art, and placed into service.

Hydroisomerization Catalysts

In an embodiment, processes of the present invention use a layeredcatalyst system comprising a first hydroisomerization catalyst and asecond hydroisomerization catalyst, wherein the first hydroisomerizationcatalyst may be disposed upstream from the second hydroisomerizationcatalyst. In an embodiment, both of the first and secondhydroisomerization catalysts may be selective for the isomerization ofn-paraffins in the hydrocarbon feed. In an embodiment, the first andsecond hydroisomerization catalysts have different formulations, and mayhave different levels of isomerization selectivity. In an embodiment,the first hydroisomerization catalyst may have a higher level ofselectivity for the isomerization of n-paraffins as compared with thesecond hydroisomerization catalyst.

Each of the first and second hydroisomerization catalysts may comprise amolecular sieve and a Group VIII metal. In an embodiment, the molecularsieve of each of the first hydroisomerization catalyst and the secondhydroisomerization catalyst may comprise a 1-D, 10-ring molecular sieve.The Group VIII metal of the first and second hydroisomerizationcatalysts may comprise platinum, palladium, or a combination thereof. Inan embodiment, each of the first and second hydroisomerization catalystsmay comprise from about 0.1 to about 1.5 wt % of the Group VIII metal,typically from about 0.2 to about 1.0 wt %, and usually from about 0.325to about 1.0 wt % of the Group VIII metal. In an embodiment, at leastone of the first hydroisomerization catalyst and the secondhydroisomerization catalyst may further comprise a metal modifierselected from the group consisting of Mg, Ca, Sr, Ba, K, La, Pr, Nd, Cr,and combinations thereof, substantially as described hereinbelow.

Typically, each of the first and second hydroisomerization catalystswill still further comprise a support or binder. The support maycomprise a refractory inorganic oxide. Suitable inorganic oxide supportsfor the hydroisomerization catalysts include silica, alumina, titanic,magnesia, zirconia, silica-alumina, silica-magnesia, silica-titanic, andthe like, and combinations thereof. Each of the first hydroisomerizationcatalyst and the second hydroisomerization catalyst may comprise fromabout 5 to about 95 wt % or more of the molecular sieve component,typically from about 15 to about 85 wt % of the molecular sieve, andusually from about 25 to about 75 wt % of the molecular sieve.Generally, it is advantageous to minimize the molecular sieve componentfor economic reasons, provided that the catalyst retains the requiredactivity and selectivity levels. Each of the first hydroisomerizationcatalyst and the second hydroisomerization catalyst may comprise fromabout 0 to about 95 wt % of the support material, and more typicallyfrom about 5 to about 90 wt %.

In an exemplary catalyst system for dewaxing hydrocarbon feedstocksaccording to processes of the present invention, each of the firsthydroisomerization catalyst and the second hydroisomerization catalystmay comprise a 1-D, 10-ring molecular sieve and a Group VIII metal. Themolecular sieve of at least one of the first hydroisomerization catalystand the second hydroisomerization catalyst may comprise a medium porezeolite, e.g., a zeolite having a pore aperture in the range from about0.39 nm to about 0.7 nm. In an embodiment, each of the firsthydroisomerization catalyst and the second hydroisomerization catalystmay further comprise from about 0.325 wt % to about 1 wt % platinum.

Examples of molecular sieves that may be useful in formulating at leastone of the first and second hydroisomerization catalysts includemolecular sieves of the AEL framework type code, such as SAPO-11,SAPO-31, SM-3, SM-6; as well as zeolite type materials of the MTT or TONcodes. Molecular sieves of the MTT code include ZSM-23, SSZ-32, EU-13,ISI-4, and KZ-1. Molecular sieves of the TON code that may be useful inpracticing the present invention include Theta-1, ISI-1, KZ-2, NU-10,and ZSM-22. The parameters of MTT and TON type molecular sieves arefurther described in the Atlas of Zeolite Framework Types which ispublished by the International Zeolite Association (IZA). In anembodiment, at least one of the first hydroisomerization catalyst andthe second hydroisomerization catalyst may comprise zeolite SSZ-32x. Ina subembodiment, the first hydroisomerization catalyst may compriseSSZ-32x. In another subembodiment, the second hydroisomerizationcatalyst may comprise zeolite SSZ-32. Processes of the present inventionare not limited to any particular hydroisomerization catalystformulations.

Zeolite SSZ-32x

According to one embodiment of the instant invention, a layered catalystsystem for dewaxing a hydrocarbon feed contains an MTT framework typemolecular sieve designated zeolite SSZ-32x. SSZ-32x and methods formaking SSZ-32x are described in U.S. Pat. No. 7,390,763 to Zones, issuedAug. 4, 2009.

As determined by TEM studies, crystallites of SSZ-32x prepared accordingto the present invention are generally elongate with a length/widthratio typically in the range from about 2.0 to about 2.4, and have alength typically in the range from about 15 nm to about 20 nm, and awidth typically in the range from about 7 nm to about 9 nm.

Metal Loading of Catalysts

In an embodiment, at least one of the first hydroisomerization catalystand the second hydroisomerization catalyst may further comprise one ormore metal modifier(s). In a sub-embodiment, both the firsthydroisomerization catalyst and the second hydroisomerization catalystmay each comprise a metal modifier. Typically, the metal modifier(s) maybe selected from the group consisting of Mg, Ca, Sr, Ba, K, La, Pr, Nd,Cr, and combinations thereof. In a sub-embodiment, the metal modifiermay comprise Mg. In an embodiment, a metal-modified catalyst of thepresent invention may comprise from about 0.5 to about 3.5 wt % of Mg orother metal modifier(s), typically from about 0.5 to about 2.5 wt %, andusually from about 0.9 to about 2.5 wt % of Mg or other metalmodifier(s).

In another embodiment, the second (e.g., downstream) hydroisomerizationcatalyst may substantially lack a metal modifier. Stated differently, inan embodiment a metal modifier component selected from the groupconsisting of Mg, Ca, Sr, Ba, K, La, Pr, Nd and Cr may be included inthe first hydroisomerization catalyst, but omitted from the secondhydroisomerization catalyst. As a non-limiting example, the firsthydroisomerization catalyst may comprise zeolite SSZ-32x; a Group VIIInoble metal, such as platinum; and a metal modifier such as magnesium.In contrast, the second hydroisomerization catalyst may consistessentially of a 1-D, 10-ring molecular sieve (e.g., SSZ-32 or SSZ-32x),a Group VIII metal, and a refractory oxide support.

In formulating a catalyst or catalyst system for dewaxing processes ofthe present invention, a mixture of a molecular sieve and an oxidebinder may be formed into a particle or extrudate having a wide range ofphysical shapes and dimensions. In an embodiment, the extrudate orparticle may be dried and calcined prior to metal loading. Calcinationmay be performed at temperatures typically in the range from about 390°F. to about 1100° F. for periods of time ranging from about 0.5 to about5 hours, or more. The calcined extrudate or formed particle may then beloaded with at least one metal modifier selected from the groupconsisting of Ca, Cr, Mg, La, Na, Pr, Sr, K, Nd, and combinationsthereof. While not being bound by theory, such metals may effectivelyreduce the number of acid sites on the molecular sieve of themetal-modified hydroisomerization catalyst, thereby increasing thecatalyst's selectivity for isomerization (versus cracking) ofn-paraffins in the feed.

The loading of modifying metal(s) on the catalyst(s) may be accomplishedby techniques known in the art, such as by impregnation or ion exchange.Ion exchange techniques typically involve contacting the extrudate orparticle with a solution containing a salt of the desired metalcation(s). A variety of metal salts, such as halides, nitrates, andsulfates, may be used in this regard. Following contact with a saltsolution of the desired metal cation(s), the extrudate or particle maybe dried, e.g., at temperatures in the range from about 150° F. to about800° F. The extrudate or particle may thereafter be further loaded witha Group VIII metal component of the catalyst.

In an embodiment, a molecular sieve or catalyst of the invention may beco-impregnated with a modifying metal and a Group VIII metal. Afterloading the Group VIII and modifying metals, the catalyst may becalcined in air or inert gas at temperatures in the range from about500° F. to about 900° F. The preparation of molecular sieve catalystscomprising a metal modifier is disclosed in commonly assigned U.S. Pat.No. 7,141,529 and in U.S. Publication No. 20080083657 (Zones et al.),the disclosure of each of which is incorporated by reference herein inits entirety.

Dewaxing Catalyst Systems

According to an embodiment of the present invention, a dewaxing catalystsystem 10 for the production of base oils from a hydrocarbon feedstockmay be described with reference to FIG. 1, as follows. Catalyst system10 may be a layered system comprising a plurality of hydroisomerizationcatalyst layers. In an embodiment, each of the layers ofhydroisomerization catalyst may have a different formulation, activity,and/or n-paraffin isomerization selectivity. By “n-paraffinisomerization selectivity” is meant the propensity of a given catalystto isomerize, as opposed to crack, n-paraffins in the feedstock.

Catalyst system 10 may include a hydrotreating zone or guard layer 12, afirst hydroisomerization zone 14, and a second hydroisomerization zone16. Guard layer 12, first hydroisomerization zone 14, and secondhydroisomerization zone 16 may contain, respectively, a hydrotreatingcatalyst 18, a first hydroisomerization catalyst 20, and a secondhydroisomerization catalyst 22. Guard layer 12 may be disposed upstreamfrom first hydroisomerization catalyst 20, and first hydroisomerizationcatalyst 20 may be disposed upstream from second hydroisomerizationcatalyst 22. In an embodiment as shown in FIG. 1, guard layer 12, firsthydroisomerization zone 14, and second hydroisomerization zone 16 may behoused within a single reactor 24. Although the invention has beendescribed with reference to FIG. 1 as comprising two hydroisomerizationzones and a guard layer, other numbers of zones and layers are alsopossible under the present invention.

A hydrocarbon feed 26 may be introduced into reactor 24 via a firstconduit 28 a, while hydrogen gas may be introduced into reactor 24 via asecond conduit 28 b.

Within reactor 24, feed 26 may be contacted with hydrotreating catalyst18 in the presence of hydrogen to provide a hydrotreated feedstock 30.Hydrotreated feedstock 30 may be contacted with first hydroisomerizationcatalyst 20 under first hydroisomerization conditions in firsthydroisomerization zone 14 to provide a first isomerization stream 32.First isomerization stream 32 may be contacted with secondhydroisomerization catalyst 22 under second hydroisomerizationconditions in second hydroisomerization zone 16 to provide a secondisomerization stream 34.

Second isomerization stream 34 may be fed to a hydrofinishing unit (notshown) to provide a suitable quality and yield of the desired base oilproduct. The base oil product may have a pour point not higher thanabout −9° C., typically not higher than about −12° C., and usually nothigher than about −14° C. The base oil product may have a cloud pointnot higher than about −5° C., typically not higher than about −7° C.,and usually not higher than about −12° C. The base oil product may havea pour-cloud spread of not more than about 7° C., typically not morethan about 5° C., and usually not more than about 3° C. In anembodiment, the base oil product having the above properties may beobtained at a yield of at least 89%.

In an embodiment, hydrotreating catalyst 18 may be a high activitycatalyst capable of operating effectively at a relatively high hourlyliquid space velocity (e.g., LHSV>1 hr⁻¹) and at a temperature in therange from about 550° F. to about 750° F. The hydrotreating catalyst(guard layer) may occupy from about 3% to about 30% by volume of thetotal catalyst volume, i.e., the hydrotreating catalyst may comprisefrom about 3% to about 30% of the sum of the volume of the hydrotreatingcatalyst plus the volume of the first hydroisomerization catalyst plusthe volume of the second hydroisomerization catalyst. Typically, thehydrotreating catalyst may comprise from about 5% to about 20% of thetotal catalyst volume, and usually from about 5% to about 15% of thetotal catalyst volume.

In an embodiment, the ratio of the volume of the firsthydroisomerization catalyst to the volume of the secondhydroisomerization catalyst may be in the range from about 7:3 to about3:7, typically from about 3:2 to about 2:3, and usually from about 5:4to about 4:5. In a subembodiment, the ratio of the volume of the firsthydroisomerization catalyst to the volume of the secondhydroisomerization catalyst may be about 1:1.

Feed for Base Oil Production

The instant invention may be used to dewax a wide variety of light,medium, and/or heavy hydrocarbon feedstocks, including whole crudepetroleum, reduced crudes, vacuum tower residua, cycle oils, syntheticcrudes, gas oils, vacuum gas oils, foots oils, Fischer-Tropsch derivedwaxes, and the like. In an embodiment, the hydrocarbon feedstocks can bedescribed as waxy feeds having pour points generally above about 0° C.,and having a tendency to solidify, precipitate, or otherwise form solidparticulates upon cooling to about 0° C. Straight chain n-paraffins,either alone or with only slightly branched chain paraffins, having 16or more carbon atoms may be referred to herein as waxes. The feedstockwill usually be a C₁₀₊ feedstock generally boiling above about 350° F.

Typical feedstocks may include hydrotreated or hydrocracked gas oils,hydrotreated lube oil raffinates, brightstocks, lubricating oil stocks,synthetic oils, foots oils, Fischer-Tropsch synthesis oils, high pourpoint polyolefins, normal alphaolefin waxes, slack waxes, deoiled waxesand microcrystalline waxes. Other hydrocarbon feedstocks suitable foruse in processes of the present invention may be selected, for example,from gas oils and vacuum gas oils; residuum fractions from anatmospheric pressure distillation process; solvent-deasphalted petroleumresidua; shale oils, cycle oils; animal and vegetable derived fats, oilsand waxes; petroleum and slack wax; and waxes produced in chemical plantprocesses.

In an embodiment of the present invention, the feedstock for base oilproduction may comprise a light feed. Herein, the term “light feed” maybe used to refer to a hydrocarbon feedstock wherein at least about 80%of the components have a boiling point below about 900° F. Examples oflight feeds suitable for practicing the present invention include lightneutral (100-150N) and medium neutral (200-250N). In another embodiment,the feedstock for processes of the present invention may comprise aheavy feed. Herein, the term “heavy feed” may be used to refer to ahydrocarbon feedstock wherein 80% or more of the components have aboiling point above about 900° F. Examples of heavy feeds suitable forpracticing the present invention include heavy neutral (600N) and brightstock.

The present invention may also be suitable for processing waxydistillate stocks such as middle distillate stocks including gas oils,kerosenes, and jet fuels, lubricating oil stocks, heating oils, andother distillate fractions whose pour point and viscosity need to bemaintained within certain specification limits.

Feedstocks for processes of the present invention may typically includeolefin and naphthene components, as well as aromatic and heterocycliccompounds, in addition to higher molecular weight n-paraffins andslightly branched paraffins. During processes of the present invention,the degree of cracking of n-paraffins and slightly branched paraffins inthe feed is strictly limited so that the product yield loss isminimized, thereby preserving the economic value of the feedstock.

In an embodiment, the hydrocarbon feedstocks of the present inventionmay generally have a pour point above 0° C., and in some embodimentsabove about 20° C. In contrast, the base oil products of processes ofthe present invention, resulting from hydroisomerization dewaxing of thefeedstock, generally have pour points below 0° C., typically below about−12° C., and often below about −14° C.

In an embodiment, the feedstock employed in processes of the presentinvention can be a waxy feed which contains more than about 20% wax,more than about 50% wax, or even greater than about 70% wax. Moretypically, the feed will contain from about 5% to about 30% wax. As usedherein, the term “waxy hydrocarbon feedstocks” may include plant waxesand animal derived waxes in addition to petroleum derived waxes.

According to one aspect of the present invention, a wide range of feedsmay be used to produce lubricant base oils in high yield with goodperformance characteristics, including low pour point, low cloud point,low pour-cloud spread, and high Viscosity Index. The quality and yieldof the lube base oil product of the instant invention may depend on anumber of factors, including the formulation of the hydroisomerizationcatalysts comprising the layered catalyst systems, and the configurationof the catalyst layers of the catalyst systems.

In an embodiment of the present invention, the quality and yield of thelube base oil product may depend on the orientation of the differenthydroisomerization catalysts with respect to the feed stream. As anexample, applicants have now discovered that a hydroisomerizationcatalyst having a higher level of isomerization selectivity may bedisposed upstream from a hydroisomerization catalyst having a lowerlevel of isomerization selectivity to provide base oil products withimproved characteristics and at increased yields, as compared withconventional processes and systems. Moreover, applicants have alsoobserved that the opposite orientation of the hydroisomerizationcatalysts with respect to the feed stream may provide inferior results,e.g., decreased quality and/or quantity of base oil product. By“opposite orientation” in this regard is meant a catalyst systemconfiguration wherein a hydroisomerization catalyst having a higherlevel of isomerization selectivity is disposed downstream from ahydroisomerization catalyst having a lower level of isomerizationselectivity.

Dewaxing Processes

According to one embodiment of the present invention a catalyticdewaxing process for the production of base oils from a hydrocarbonfeedstock may involve introducing the feed into a reactor containing adewaxing catalyst system. Hydrogen gas may also be introduced into thereactor so that the process may be performed in the presence ofhydrogen, e.g., as described hereinbelow with reference to the processconditions.

Within the reactor, the feed may be contacted with a hydrotreatingcatalyst under hydrotreating conditions in a hydrotreating zone or guardlayer to provide a hydrotreated feedstock. Contacting the feedstock withthe hydrotreating catalyst in the guard layer may serve to effectivelyhydrogenate aromatics in the feedstock, and to remove N- andS-containing compounds from the feed, thereby protecting the first andsecond hydroisomerization catalysts of the catalyst system. By“effectively hydrogenate aromatics” is meant that the hydrotreatingcatalyst is able to decrease the aromatic content of the feedstock by atleast about 20%. The hydrotreated feedstock may generally comprise C₁₀₊n-paraffins and slightly branched isoparaffins, with a wax content oftypically at least about 20%.

The hydrotreated feedstock may be contacted with the firsthydroisomerization catalyst under first hydroisomerization dewaxingconditions in a first hydroisomerization zone to provide a firstisomerization stream. Thereafter, the first isomerization stream may becontacted with the second hydroisomerization catalyst under secondhydroisomerization dewaxing conditions in a second hydroisomerizationzone to provide a second isomerization stream. The guard layer, thefirst hydroisomerization catalyst, and the second hydroisomerizationcatalyst may all be disposed within a single reactor. The hydrotreatingand hydroisomerization conditions that may be used for catalyticdewaxing processes of the present invention are described hereinbelow.

The second isomerization stream may be fed to a hydrofinishing unit toprovide a suitable quality and yield of the desired base oil product.Such a hydrofinishing step, may remove traces of any aromatics, olefins,color bodies, and the like from the base oil product. The hydrofinishingunit may include a hydrofinishing catalyst comprising an alumina supportand a noble metal, typically palladium, or platinum in combination withpalladium. In an embodiment, the noble metal content of thehydrofinishing catalyst may typically be in the range from about 0.1 toabout 1.0 wt %, usually from about 0.1 to about 0.6 wt %, and often fromabout 0.2 to about 0.5 wt %.

Each of the first hydroisomerization catalyst and the secondhydroisomerization catalyst may comprise a 1-D, 10-ring molecular sieveand a Group VIII metal, e.g., substantially as described hereinaboveunder “Hydroisomerization Catalysts.” Each of the firsthydroisomerization catalyst and the second hydroisomerization catalystmay be selective for the isomerization of n-paraffins in the feedstock,such that feedstock components are preferentially isomerized rather thancracked. In an embodiment, the molecular sieve of the firsthydroisomerization catalyst may comprise zeolite SSZ-32x, as describedhereinabove.

According to one aspect of the present invention, the first and secondhydroisomerization catalysts may have different levels of selectivityfor the isomerization of n-paraffins in the feedstock. In an embodiment,the first hydroisomerization catalyst may be more selective for theisomerization of n-paraffins in the feedstock as compared with thesecond hydroisomerization catalyst (see, e.g., FIG. 2A). Stateddifferently, in an embodiment of the present invention the firsthydroisomerization catalyst may have a first level of selectivity forthe isomerization of n-paraffins in the feedstock and the secondhydroisomerization catalyst may have a second level of selectivity forthe isomerization of n-paraffins in the feedstock, wherein the firstlevel of selectivity may be higher than the second level of selectivity.

FIG. 2A schematically represents a layered dewaxing catalyst system 10A,according to an embodiment of the present invention. Catalyst system 10Acomprises a first hydroisomerization catalyst 120 disposed upstream froma second hydroisomerization catalyst 122. In an embodiment, firsthydroisomerization catalyst 120 may have a higher level of selectivityfor the isomerization of n-paraffins as compared with secondhydroisomerization catalyst 122. FIG. 2B schematically represents alayered dewaxing catalyst system 10B having the same composition, butthe opposite orientation as compared with catalyst system 10A of FIG.2A, i.e., in catalyst system 10B hydroisomerization catalyst 120 isdisposed downstream from hydroisomerization catalyst 122.

With further reference to FIGS. 2A-B, a waxy hydrocarbon feed may becontacted with hydroisomerization catalysts 120 and 122 in the presenceof hydrogen to provide a base oil product. In particular, catalystsystem 10A provides a dewaxed product A, while catalyst system 10Bprovides a dewaxed product B, wherein product A is, surprisingly,substantially superior to product B. Accordingly, applicants have foundthat the combination of first hydroisomerization catalyst 120 disposedupstream from second hydroisomerization catalyst 122 (e.g., FIG. 2A) canprovide a superior base oil product, as compared with the inverseconfiguration (FIG. 2B).

According to another aspect of the present invention, applicants havealso found that the combination of the first hydroisomerization catalystupstream from the second hydroisomerization catalyst can provide equalor superior results, as compared with the same volume of catalyst ofeither the first hydroisomerization catalyst alone or the secondhydroisomerization catalyst alone.

The superior results referred to hereinabove with respect to the use oflayered catalyst systems for lube oil production may be manifest notonly as increased product yield but also improved product qualities.

FIG. 3A schematically represents a first catalytic dewaxing system 100Adisposed in a reactor 24, wherein dewaxing system 100A may consistessentially of a first hydroisomerization catalyst 220. FIG. 3Bschematically represents a second catalytic dewaxing system 100Bdisposed in a reactor 24, wherein dewaxing system 100B may consistessentially of a second hydroisomerization catalyst 222. Firsthydroisomerization catalyst 220 and second hydroisomerization catalyst222 may have, respectively, first and second levels of selectivity forthe isomerization of n-paraffins. In an embodiment, the first and secondlevels of selectivity may be similar or at least substantially the same.Systems 100A and 100B may provide a dewaxed product A′ and a dewaxedproduct B′, respectively, by dewaxing a hydrocarbon feed in the presenceof hydrogen, wherein the yield of products A′ and B′ may be at leastsubstantially the same. The hydrocarbon feed may be a light, medium, orheavy feed. Optionally, systems 100A and 100B may include a guard layer.

FIG. 3C schematically represents a layered dewaxing catalyst system100C, according to an embodiment of the present invention. Catalystsystem 100C may comprise first hydroisomerization catalyst 220 disposedupstream from second hydroisomerization catalyst 222. In an embodiment,catalyst system 100C may have a third level of selectivity for theisomerization of n-paraffins, wherein the third level of selectivity maybe higher than each of the first level of selectivity of catalyst 220and the second level of selectivity of catalyst 222. As a result, system100C may provide a dewaxed product C′ at a significantly higher yield,for a given cloud point, as compared with the yield of either product A′or product B′. In an embodiment, layered dewaxing system 100C mayinclude a guard layer disposed upstream from first hydroisomerizationcatalyst 120 (see, for example, FIG. 1).

Thus, according to an embodiment of the present invention, applicantshave found that the combination of first and second hydroisomerizationcatalysts 220 and 222 (see, e.g., FIG. 3C) can provide superior results,as compared with the use of the same volume of either firsthydroisomerization catalyst 220 alone or second hydroisomerizationcatalyst 222 alone. Such superior results may be manifest not only asincreased product yield but also improved product qualities.

Reaction Conditions

The conditions under which processes of the present invention arecarried out will generally include a temperature within a range fromabout 390° F. to about 800° F. In an embodiment, each of the first andsecond hydroisomerization dewaxing conditions includes a temperature inthe range from about 550° F. to about 700° F. In a further embodimentthe temperature may be in the range from about 590° F. to about 675° F.The pressure may be in the range from about 15 to about 3000 psig, andtypically in the range from about 100 to about 2500 psig.

Typically, the feed rate to the catalyst system/reactor during dewaxingprocesses of the present invention may be in the range from about 0.1 toabout 20 hr⁻¹ LHSV, and usually from about 0.1 to about 5 hr⁻¹ LHSV.Generally, dewaxing processes of the present invention are performed inthe presence of hydrogen. Typically, the hydrogen to hydrocarbon ratiomay be in a range from about 2000 to about 10,000 standard cubic feet H₂per barrel hydrocarbon, and usually from about 2500 to about 5000standard cubic feet H₂ per barrel hydrocarbon.

The above conditions may apply to the hydrotreating conditions of thehydrotreating zone as well as to the hydroisomerization conditions ofthe first and second hydroisomerization zones (see, for example, FIG.1). The reactor temperature and other process parameters may varyaccording to factors such as the nature of the hydrocarbon feedstockused and the desired characteristics (e.g., pour point, cloud point, VI)and yield of the base oil product.

The hydrotreating catalyst may be disposed upstream from thehydroisomerization catalysts and in the same reactor as thehydroisomerization catalysts. In an embodiment, a temperature differencemay exist between the first and second hydroisomerization zones. Forexample, the first hydroisomerization zone may be at a first temperatureand the second hydroisomerization zone may be at a second temperature,wherein the second temperature may be from about 20° F. to about 60° F.higher than the first temperature, more typically from about 30° F. toabout 50° F. higher, and usually from about 35° F. to about 45° F.higher than the first temperature.

The effluent or stream from a catalyst system of the present invention,e.g., the second hydroisomerization stream from the secondhydroisomerization zone, may be further treated by hydrofinishing. Suchhydrofinishing may be performed in the presence of a hydrogenationcatalyst, as is known in the art. The hydrogenation catalyst used forhydrofinishing may comprise, for example, platinum, palladium, or acombination thereof on an alumina support. The hydrofinishing may beperformed at a temperature in the range from about 400° F. to about 650°F., and a pressure in the range from about 400 psig to about 4000 psig.Hydrofinishing for the production of lubricating oils is described, forexample, in U.S. Pat. No. 3,852,207, the disclosure of which isincorporated by reference herein.

Base Oil Product

In an embodiment, processes of the invention provide a high value, highquality lubricant oil in good yield from a low value waxy hydrocarbonfeedstock. The lubricant oils of the present invention will typicallyhave a pour point less than about 9° C., usually less than about −12°C., and often less than about −14 C, e.g., as measured by ASTM D-97. Inan embodiment, the lubricant oil product may have a pour point in therange from about −10° C. to about −30° C. The products of the presentinvention will generally have viscosities in the range of 3 to 30 cSt at100° C., and a VI in the range from about 95 to about 170 as measured byASTM D445.

As noted hereinabove, the dewaxed second hydroisomerization stream(FIG. 1) may be further hydrotreated, for example, over one or morehydrofinishing catalysts to obtain a final lubricant oil product havingthe desired characteristics. As an example, at least a portion of thesecond hydroisomerization stream may be hydrofinished to remove anycolored materials and/or to hydrogenate any aromatic species in order tomeet the desired lubricant oil specifications and/or to improve thestability of the base oil product.

The following Examples illustrate but do not limit the presentinvention.

EXAMPLES Syntheses of Zeolite SSZ-32x Example 1

A reaction mixture for the synthesis of SSZ-32x was prepared by addingin sequence to deionized water the following: KOH (45.8%, Fisher),

0.47M N,N′-diisopropylimidazolium hydroxide (DIPI), and alumina-coatedsilica DVSZN007 (SAR=35; 25.22% solids (Nalco, Naperville, Ill.)). Themolar ratios of the reaction mixture components were as follows:

Components Molar ratio SiO₂/Al₂O₃ 35.0 H₂0/SiO₂ 33.86 OH⁻/SiO₂ 0.28KOH/SiO₂ 0.24 DIPI/SiO₂ 0.04

The reaction mixture was heated to 170° C. with an 8 hour ramp andcontinuously stirred at 150 rpm for 135 hours. The product wasdetermined via powder XRD analysis to be SSZ-32x. The reaction time forsynthesis of SSZ-32x can be considerably shortened by the inclusion ofseed crystals in the reaction mixture, see for example, Examples 2 and3.

Example 2

A reaction mixture for the synthesis of SSZ-32x was prepared by addingthe same components as in Example 1, except SSZ-32x slurry seeds (3.15wt % SSZ-32x based on the SiO₂ content) were included in the reactionmixture. Seed crystals were obtained from a prior SSZ-32x preparationthat did not include slurry seeds (see, e.g., Example 1). The molarratios of the reaction mixture components were as follows:

Components Molar Ratio SiO₂/Al₂O₃ 35.00 H₂0/SiO₂ 31.00 OH⁻/SiO₂ 0.27KOH/SiO₂ 0.23 DIPI/SiO₂ 0.04 % Seed 3.15%

The reaction mixture was heated to 170° C. with an 8 hour ramp andcontinuously stirred at 150 rpm. The reaction endpoint was realized at areaction time (at temperature) of about 60 hours. The product wasconfirmed by powder XRD analysis to be SSZ-32x.

Example 3

Another sample of SSZ-32x was synthesized by preparing a reactionmixture, substantially as described in Example 2, to provide a reactionmixture having component molar ratios as follows:

Components Molar Ratio SiO₂/Al₂O₃ 35.00 H₂0/SiO₂ 33.00 OH⁻/SiO₂ 0.27KOH/SiO₂ 0.21 DIPI/SiO₂ 0.06 % Seed 3.5%

The amount of SSZ-32x seeds used in the reaction mixture was 3.5 wt %based on the SiO₂ content. The reaction conditions were as described inExample 2. The SSZ-32x product of Example 3 was calcined inside a mufflefurnace under a flow of 2% oxygen/98% nitrogen, ammonium exchanged usingNH₄NO₃, washed and dried. The XRD data of calcined SSZ-32x preparedaccording to Example 3 is shown in Table 4.

Example 4 Hexadecane Isomerization

The SSZ-32x preparations of Examples 2 and 3 were tested for theirisomerization selectivity using n-hexadecane as feed and proceduressubstantially as described in Example 10 of U.S. Pat. No. 7,063,828. Thepercent isomerization selectivity and C⁴⁻ cracking at 96% n-C₁₆conversion for the two preparations are shown in Table 5.

TABLE 5 Hexadecane Isomerization at 96% Conversion Example IsomerizationC₄ minus No. Selectivity Cat. ° F. Cracking 2 81% 527 2.4% 3 81% 5222.3%

Example 5 Dewaxing Catalyst Preparation

Hydroisomerization catalyst A was prepared as follows. Small (e.g., ca.15-20 nm) crystallite SSZ-32x was composited with alumina to provide amixture containing 45 wt % zeolite, and the mixture was extruded, dried,and calcined. The dried and calcined extrudate was impregnated with asolution containing both platinum and magnesium, and the co-impregnatedcatalyst was then dried and calcined. The overall platinum loading was0.325 wt %, and the magnesium loading was 2.5 wt %.

Hydroisomerization catalyst B was prepared as described for catalyst Ato provide a mixture containing 45 wt % zeolite. The dried and calcinedextrudate was impregnated with platinum to give a platinum loading of0.325 wt %.

Hydroisomerization catalyst C was prepared generally as described forcatalyst A, except the mixture contained 65 wt % zeolite. The dried andcalcined extrudate was co-impregnated with platinum and magnesium togive a platinum loading of 0.325 wt % and a magnesium loading of 0.9 wt%.

Example 6 Comparative Catalytic Dewaxing Using Catalyst System A/B

A layered hydroisomerization dewaxing catalyst system A/B was preparedby disposing a layer of catalyst A on a layer of catalyst B, such thatcatalyst A was the upper layer, i.e., catalyst A was disposed upstreamfrom catalyst B. A guard layer comprising alumina loaded with 0.3 wt %Pt and 0.6 wt % Pd was disposed upstream from catalyst system A/B. Thelayered catalyst system A/B was compared with an equal volume ofcatalyst A alone in dewaxing a waxy heavy hydrocrackate (600N) feed.Following isomerization, the dewaxed products were separatelyhydrofinished over a Pt/Pd silica-alumina hydrofinishing catalyst. Thelayered catalyst system A/B unexpectedly gave an increase in yield atthe target cloud point as compared with the same volume of catalyst Aalone.

Example 7 Comparative Catalytic Dewaxing Using Catalyst System A/C

A layered hydroisomerization dewaxing catalyst system A/C was preparedby disposing a layer of catalyst A on a layer of catalyst C, such thatcatalyst A was the upper layer, i.e., catalyst A was disposed upstreamfrom catalyst C. A guard layer comprising alumina loaded with Pt and Pdwas disposed upstream from catalyst system A/C. The layered catalystsystem A/C was compared with an equal volume of catalyst A alone indewaxing a waxy heavy hydrocrackate (600N) feed. Followingisomerization, the dewaxed products were separately hydrofinished over aPt/Pd silica-alumina hydrofinishing catalyst. The layered catalystsystem A/C unexpectedly gave an increase in yield at the target cloudpoint as compared with the same volume of catalyst A alone.

Numerous variations of the present invention may be possible in light ofthe teachings and examples herein. It is therefore understood thatwithin the scope of the following claims, the invention may be practicedotherwise than as specifically described or exemplified herein.

What is claimed is:
 1. A process for catalytically dewaxing a waxyhydrocarbon feedstock, comprising: a) contacting the hydrocarbonfeedstock in a first hydroisomerization zone under firsthydroisomerization dewaxing conditions with a first hydroisomerizationcatalyst comprising SSZ-32x to provide a first isomerization stream; andb) contacting at least a portion of the first isomerization stream in asecond hydroisomerization zone under second hydroisomerization dewaxingconditions with a second hydroisomerization catalyst which comprises amolecular sieve and a Group VIII metal to provide a second isomerizationstream.
 2. The process according to claim 1, wherein the secondhydroisomerization catalyst comprises a 1-D, 10-ring molecular sieve. 3.The process according to claim 1, wherein the first hydroisomerizationcatalyst comprises SSZ-32x doped with a metal modifier selected from thegroup consisting of Mg, Ca, Sr, Ba, K, La, Pr, Nd, Cr, and combinationsthereof.
 4. The process according to claim 3, wherein the firsthydroisomerization catalyst has a first level of selectivity for theisomerization of n-paraffins in the feedstock, the secondhydroisomerization catalyst has a second level of selectivity for theisomerization of n-paraffins in the feedstock, and wherein the firstlevel of selectivity is higher than the second level of selectivity. 5.The process according to claim 3, wherein the metal modifier comprisesMg at a concentration in the range from about 0.5 to about 2.5 wt. %. 6.The process according to claim 3, wherein the second hydroisomerizationcatalyst at least substantially lacks a metal modifier.
 7. The processaccording to claim 1, wherein at least about 80% of the feedstockcomponents have a boiling point below about 900° F. (482° C.).
 8. Theprocess according to claim 1, wherein each of the firsthydroisomerization catalyst and the second hydroisomerization catalystis doped with a metal modifier selected from the group consisting of Mg,Ca, Sr, Ba, K, La, Pr, Nd, Cr, and combinations thereof.
 9. The processaccording to claim 1, wherein the first hydroisomerization catalyst andthe second hydroisomerization catalyst are disposed within a singlereactor.
 10. The process according to claim 1, further comprising: c)prior to step a), contacting the hydrocarbon feedstock in ahydrotreating zone under hydrotreating conditions with a hydrotreatingcatalyst, wherein the hydrotreating catalyst occupies a volume in therange from about 3% to about 30% of the total volume of thehydrotreating catalyst, the first hydroisomerization catalyst, and thesecond hydroisomerization catalyst.
 11. The process according to claim1, wherein the ratio of the volume of the first hydroisomerizationcatalyst to the volume of the second hydroisomerization catalyst is inthe range from about 3:2 to about 2:3.
 12. The process according toclaim 1, further comprising: c) contacting the second isomerizationstream with a hydrofinishing catalyst in the presence of hydrogen toprovide a base oil product having a pour point of not more than about−12° C., and a pour-cloud spread of not more than about 5° C.
 13. Theprocess according to claim 1, wherein the first hydroisomerizationcatalyst comprises from about 5 to about 95 wt. % SSZ-32x and from about0.1 to about 1.0 wt. % of Group VIII metal.
 14. A process forcatalytically dewaxing a waxy hydrocarbon feedstock, comprising: a)contacting the hydrocarbon feedstock in a first hydroisomerization zoneunder first hydroisomerization dewaxing conditions with a firsthydroisomerization catalyst comprising SSZ-32x to provide a firstisomerization stream; and b) contacting at least a portion of the firstisomerization stream in a second hydroisomerization zone under secondhydroisomerization dewaxing conditions with a second hydroisomerizationcatalyst to provide a second isomerization stream, wherein the firsthydroisomerization catalyst further comprises a Group VIII metal, thesecond hydroisomerization catalyst comprises a 1-D, 10-ring zeolite anda Group VIII metal, at least one of the first hydroisomerizationcatalyst and the second hydroisomerization catalyst is doped with ametal modifier selected from the group consisting of Mg, Ca, Sr, Ba, K,La, Pr, Nd, Cr, and combinations thereof; and the first and secondhydroisomerization catalysts are disposed in the same reactor.
 15. Theprocess according to claim 14, further comprising: c) contacting thesecond isomerization stream with a hydrofinishing catalyst in thepresence of hydrogen to provide a base oil product having a pour pointof not more than about −12° C., and a pour-cloud spread of not more thanabout 5° C.
 16. The process according to claim 14, wherein the firsthydroisomerization catalyst is doped with the metal modifier, the firsthydroisomerization catalyst has a first level of selectivity for theisomerization of n-paraffins in the feedstock, the secondhydroisomerization catalyst has a second level of selectivity for theisomerization of n-paraffins in the feedstock, and wherein the firstlevel of selectivity is higher than the second level of selectivity. 17.A layered catalyst system, comprising: a first hydroisomerization zonecomprising a first hydroisomerization catalyst comprising SSZ-32x; and asecond hydroisomerization zone comprising a second hydroisomerizationcatalyst, wherein each of the first and second hydroisomerizationcatalysts comprises a molecular sieve and a Group VIII metal, and themolecular sieve of at least one of the first hydroisomerization catalystand the second hydroisomerization catalyst is doped with a metalmodifier selected from the group consisting of Mg, Ca, Sr, Ba, K, La,Pr, Nd, Cr, and combinations thereof.
 18. The layered catalyst systemaccording to claim 17, wherein the first hydroisomerization catalystcomprises SSZ-32x doped with the metal modifier, the firsthydroisomerization catalyst is disposed upstream from the secondhydroisomerization catalyst, and wherein the first hydroisomerizationcatalyst has a first level of selectivity for the isomerization ofn-paraffins, the second hydroisomerization catalyst has a second levelof selectivity for the isomerization of n-paraffins, and wherein thefirst level of selectivity is higher than the second level ofselectivity.
 19. The layered catalyst system of claim 17, wherein themolecular sieve of the second hydroisomerization catalyst comprisesSSZ-32 or SSZ-32x.
 20. The layered catalyst system of claim 17, whereinthe molecular sieve of the second hydroisomerization catalyst comprisesSSZ-32x.